The present disclosure generally relates to design of optical assembly, and specifically relates to chromatic error correction of Pancharatnam Berry Phase (PBP) liquid crystal components for optical assemblies that may be used in virtual reality (VR), augmented reality (AR) and mixed reality (MR) systems.
PBP liquid crystal components can be used as an integral part of an optical assembly in a head-mounted display (HMD) that may be part of, e.g., a VR system, an AR system, a MR system, or some combination thereof. The PBP liquid crystal components can be implemented as PBP liquid crystal gratings and PBP liquid crystal lenses. However, both types of PBP liquid crystal components have strong wavelength dependences on optical performance. For example, a PBP liquid crystal grating has strong wavelength dependence on a beam steering angle, i.e., the PBP liquid crystal grating diffracts light by an angle that depends on a wavelength of the light coming into the PBP liquid crystal grating. In an illustrative embodiment, the PBP liquid crystal grating can steer beam of light at 10 degrees for green light or green color channel (i.e., wavelength of 525 nm); a beam steering angle for red light or red color channel is larger (e.g., 12.03 degrees for wavelength of 630 nm); and a beam steering angle is smaller for blue light or blue color channel (e.g., 9.33 degrees for wavelength of 490 nm). Similarly, a PBP liquid crystal lens has strong wavelength dependence on a lens focus, i.e., the PBP liquid crystal lens focuses light to a focus that depends on a wavelength of the light coming into PBP liquid crystal lens. In an illustrative embodiment, the PBP liquid crystal lens can provide focus at 2 Diopter (500 mm) for green color channel; the focus for red color channel is shorter (e.g., 416.67 mm); and the focus for blue color channel is longer (e.g., 535.71 mm).
Thus, a steering angle of a PBP liquid crystal grating and a focus of a PBP liquid crystal lens are strongly chromatic, i.e., light that is output from an optical assembly that includes one or more PBP liquid crystal components features chromatic aberration. This reduces image quality in any imaging system that employs an optical assembly with PBP liquid crystal components and a light source that emits light of multiple wavelengths or color channels.